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Design status of the ultra-low emittance synchrotron facility PETRA IV
No full textAt DESY the Synchrotron Light Source PETRA III offers scientists outstanding opportunities for experiments with hard X-rays of exceptionally high brilliance since 2009. Research activities have been started to upgrade PETRA III to the ultra-low emittance source PETRA IV, which will be diffraction limited up to the hard X-ray range. Therefore the future light source PETRA IV will be ideal for 3D X-ray microscopy of biological, chemical, and physical processes under realistic conditions at length scales from atomic dimensions to millimeters. The lattice design is aiming for a horizontal emittance in the range between 10 pm rad and 30 pm rad at a beam energy of 6 GeV. Presently, two different approaches are considered for the lattice design: a design based on a hybrid multibend achromat with an interleaved sextupole configuration based on the ESRF-EBS design, and a lattice with a double non-interleaved sextupole configuration. The current status of the design activities is reported including the injector and several technical aspects
In Situ Studies of the Electrochemical Reduction of a Supported Ultrathin Single-Crystalline (110) Layer in an Acidic Environment
No full textWith in situ surface X-ray diffraction (SXRD)and X-ray reflectivity (XRR) in combination with ex situcharacterization by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and cyclic voltamme-try, the electrochemical reduction of an ultrathin (1.66 nmthick) single-crystalline RuO(110) layer supported onRu (0001) is studied in an acidic environment, providingclear-cut evidence and mechanistic details for the trans-formation of RuO to hydrous RuO and metallic Ru. The reduction process proceeds via proton insertion into the RuO (110)lattice. For electrode potentials (0 to−50 mV vs standard hydrogen electrode), the layer spacing of RuO2(110) increased,maintaining the octahedral coordination of Ru (SXRD). Continuous proton insertion at−100 to−150 mV leads to thetransformation of the lattice oxygen of RuO to OH and water, which destroys the connectivity among the Ru-O6octahedronsand eventually leads to the loss of crystallinity (SXRD) in the RuO (110)film at−200 mV accompanied by a swelling of thelayer with a well-defined thickness (XRR). During the protonation process, soluble Ru complexes may form. With XPS thetransformation of RuO (110) to a hydrous RuO layer is followed, a process that proceedsfirst homogeneously and at highercathodic potentials heterogeneously by re-deposition of previously electrochemically dissolved Ru complexes
Impact of Preparation Method and Hydrothermal Aging on Particle Size Distribution of and Its Performance in CO and NO Oxidation
No full textThe influence of the preparation method and the corresponding particle size distribution on hydrothermal deactivation behavior at 600-800°C and its performance during CO/NO oxida-tion was systematically investigated for a series of Pt/Al2O3 catalysts. Representative conven-tional (incipient wetness impregnation) and advanced preparation methods (flame spray pyrol-ysis, supercritical fluid reactive deposition and laser ablation in liquid) were selected, which generated samples containing narrow and homogeneous but also heterogeneous particle size distributions. Basic characterization was conducted by inductively coupled plasma-optical emission spectrometry, N2 physisorption and X-ray diffraction. The particle size distribution and the corresponding oxidation state was analyzed using transmission electron microscopy and X-ray absorption spectroscopy. The systematic study shows that oxidized Pt nanoparticles smaller than 2 nm sinter very fast, already at 600°C, but potential chlorine traces from the cat-alyst precursor seem to stabilize Pt nanoparticles against further sintering and consequently maintain the catalytic performance. Samples prepared by flame spray pyrolysis and laser abla-tion showed a superior hydrothermal resistance of the alumina support, although, due to small inter-particle distance in case of laser synthesized particles, the particle size distribution in-creases considerably at high temperatures. Significant deceleration of the noble metal sintering process was obtained for the catalysts containing homogeneously distributed but slightly larg-er Pt nanoparticles (supercritical fluid reactive deposition) or for particles deposited on a ther-mally stable alumina support (flame spray pyrolysis). The correlations obtained between Pt particle size distribution, oxidation state and catalytic performance indicate different trends for CO and NO oxidation reactions, in line with structure sensitivity
Coexistence of hcp and bct Phases during In Situ Superlattice Assembly from Faceted Colloidal Nanocrystals
No full textWe study the in situ self-assembly of faceted PbS nanocrystals from colloidal suspensions upon controlled solvent evaporation using time-resolved small-angle X-ray scattering and X-ray cross-correlation analysis. In our bulk-sensitive experiment in transmission geometry, the superlattice crystallization is observed in real time, revealing a hexagonal closed-packed (hcp) structure followed by formation of a body-centered cubic (bcc) superlattice. The bcc superlattice undergoes continuous tetragonal distortion in the solvated state shortly after its formation, resulting in the body-centered tetragonal (bct) structure. Upon solvent evaporation, the bct superstructure becomes more pronounced with the still coexisting hcp phase. These findings corroborate the existing simulations of assembling cuboctahedral-shaped particles and illustrate that we observed the predicted equilibrium states. This work is essential for a deeper understanding of the fundamental forces that direct nanocrystal assembly including nanocrystal shape and ligand coverage
Dynamical emergence of scalaron in Higgs inflation
No full textWe point out that a light scalaron dynamically emerges if scalar fields have a sizable non-minimal coupling to the Ricci scalar as in the Higgs inflation model. We support this claim in two ways. One is based on the renormalization group equation; the non-minimal coupling inevitably induces a Ricci scalar quadratic term due to the renormalization group running. The other is based on scattering amplitudes; a scalar four-point amplitude develops a pole after summing over a certain class of diagrams, which we identify as the scalaron. Our result implies that the Higgs inflation is actually a two-field inflationary model. Another implication is that the Higgs inflation does not suffer from the unitarity issue since the scalaron pushes up the cut-off scale to the Planck scale
Metal-triggered conformational reorientation of a self-peptide bound to a disease-associated HLA-B*27 subtype
No full textConformational changes of major histocompatibility complex (MHC) antigens have the potential to be recognized by T cells and may arise from polymorphic variation of the MHC molecule, the binding of modifying ligands, or both. Here, we investigated whether metal ions could affect allele-dependent structural variation of the two minimally distinct human leukocyte antigen (HLA)-B*27:05 and HLA-B*27:09 subtypes, which exhibit differential association with the rheumatic disease ankylosing spondylitis (AS). We employed NMR spectroscopy and X-ray crystallography coupled with ensemble refinement to study the AS-associated HLA-B*27:05 subtype and the AS-nonassociated HLA-B* 27:09 in complex with the self-peptide pVIPR (RRKWRRWHL). Both techniques revealed that pVIPR exhibits a higher degree of flexibility when complexed with HLA-B*27:05 than with HLA-B*27:09. Furthermore, we found that the binding of the metal ion Cu2+ or Ni2+, but not Mn2+, Zn2+, or Hg2+, affects the structure of a pVIPR-bound HLA-B*27 molecule in a subtype-dependent manner. In HLA-B*27:05, the metals triggered conformational reorientations of pVIPR, but no such structural changes were observed in the HLA-B*27:09 subtype, with or without bound metal ion. These observations provide the first demonstration that not only major histocompatibility complex class II, but also class I, molecules can undergo metal ion–induced conformational alterations. Our findings suggest that metals may have a role in triggering rheumatic diseases such as AS and also have implications for the molecular basis of metal-induced hypersensitivities and allergies
Mechanism Study of Carbon Coating Effects on Conversion-Type Anode Materials in Lithium-Ion Batteries: Case Study of and ZnO–MnO Composites
No full textThe carbon coating strategy is intensively used in the modification of conversion-type anode materials to improve their cycling stability and rate capability. Thus, it is necessary to elucidate the modification mechanism induced by carbon coating. For this purpose, bare ZnMn2O4, carbon-derivative-coated ZnMn2O4, and carbon-coated ZnO–MnO composite materials have been synthesized and investigated in-depth. Herein, high-temperature synchrotron radiation diffraction is used to monitor the phase transition from ZnMn2O4 to ZnO–MnO composite during the carbonization process. The electrochemical performance has been evaluated by cyclic voltammetry, galvanostatic cycling, and electrochemical impedance spectroscopy. The carbon- and carbon-derivative-coated samples display well-improved cycling stability in terms of suppressed electrode polarization, a moderate increase in resistance, and slight capacity variation. The influence of carbon coating on the intrinsic conversion process is investigated by ex situ X-ray absorption spectroscopy, which reveals the evolution of Zn and Mn oxidation states. This result confirms that the strong capacity variation of the bare ZnMn2O4 is induced not only by the reversible charge storage in the solid electrolyte interphase but also by the phase evolution of active materials. Carbon coating is an effective method to prevent the additional oxidation of MnO to Mn3O4, which leads to a stabilization of the main conversion reaction
In-situ investigation of the evolution of microstructure and texture during load reversal of commercially pure titanium using synchrotron X-ray diffraction
No full textUnderstanding of the deformation micro-mechanism as a function of grain orientation during cyclic loading is ofsignificant importance to have failure safe design of structural components made of commercially pure titanium(CP-Ti). The evolution of deformation microstructure and texture of commercially pure titanium samples withprismatic-pyramidal (orientation A) and near basal (orientation B) as initial texture along the loading directionhas been investigated during load reversal at±8% and ± 12% strain using in-situ synchrotron X-ray diffraction.The synchrotron X-ray diffraction results have been further complemented with Elastic-Plastic Self-Consistent (EPSC) simulation of the texture data and ex-situ Electron backscatter diffraction (EBSD) scan taken atthe same region. Orientation A showed partially reversible texture whereas orientation B showed non-reversibletexture with mechanical reversibility. The partial textural reversibility has been attributed to the prism to basalslip transition which toggles the c-axis between the normal and transverse direction during the tension-compressioncycle. With an increase in strain from 8 to 12%, microstrain and dislocation density in the basal plane oforientation A decreases sharply. On the other hand, for the same level of strain in orientation B, microstrainincreases but the dislocation density of basal plane shows insignificant change. The crystal orientation mapobtained from ex-situ EBSD of deformed microstructure complements to the fact indicating, with increase instrain, deformation of basal oriented grains show non-Schmid behaviour of contraction twin propagation due tolocal strain incompatibility in orientation A. On the other hand, the prism oriented grains of orientation B havemostly deformed by extension twinning, which reorients them towards basal orientation. The deformationproceeds by lateral thickening of twins due to the lower elastic stiffness of the twinned region compared to thegrain matrix. The extension twin boundaries get converted to contraction twin boundaries at higher strain duringload reversal
FCNC-free multi-Higgs-doublet models from broken family symmetries
No full textWe demonstrate how residual flavour symmetries, infrared signatures of symmetry breaking in complete models of flavour, can naturally forbid (or limit in a flavour specific way) flavour-changing neutral currents (FCNC) in multi-Higgs-doublet models (MHDM) without using mass hierarchies. We first review how this model-independent mechanism can control the fermionic mixing patterns of the Standard Model, and then implement the symmetries in the Yukawa sector of MHDM, which allows us to intimately connect the predictivity of a given flavour model with its ability to sequester FCNC. Finally, after discussing various subtleties of the approach, we sketch an toy model that realises an explicit example of these simplified constructions
Highly Sensitive Nondestructive Rare Earth Element Detection by Means of Wavelength-Dispersive X-ray Fluorescence Spectroscopy Enabled by an Energy Dispersive pn-Charge-Coupled-Device Detector
No full textDetection of rare earth elements (REE) is commonly performed with destructive techniques such as (LA)-ICPMS or coupled to a destructive sample preparation. When investigating unique geological samples, such as cometary, asteroidal, or interstellar material from sample return missions or inclusions in deep Earth diamonds, a nondestructive method is preferred. The presented nondestructive highly sensitive wavelength-dispersive X-ray fluorescence spectroscopy (WD-XRF) technique is designed to measure the L-lines of REE between 4.5 and 7 keV with a sensitivity down to the ppm level. REE fluorescence L-lines are often only separated by a few eV from neighboring XRF-lines and cannot be resolved by an energy dispersive approach especially in the presence of transition metal K-lines. In our spectrometer the characteristic X-rays emitted by the sample are dispersed by a fixed Ge(111) analyzer crystal over the active area of an energy dispersive pn-charge-coupled-device (pnCCD) detector, enabling high energy resolution detection of X-rays differentiated by their corresponding Bragg angles. The use of an energy-dispersive 2D detector enables the simultaneous acquiring of XRF-lines while eliminating any ambiguities due to potential contribution from higher order diffraction effects or other diffraction planes and thereby increases the sensitivity by reducing the (scatter) background. This detection method shows an energy resolution of 12 eV for the Ti–Kα fluorescence line and has a sensitivity down to 0.50 ppm for REE L-lines. The method was optimized specifically for the nondestructive analysis of inclusions in deep Earth diamonds, yielding in situ quantitative information about up-to-now inaccessible elemental (REE) composition patterns together with the more abundant transition metals like Ti, Cr, Mn, and Fe. This information is of great importance to decipher the role that deep Earth plays in the global carbon and fluid cycle